Mosfet with integrated schottky diode

ABSTRACT

Schottky structure fabrication includes forming two trenches in a semiconductor material. The trenches are separated from each other by a mesa. Sidewalls and a bottom surface of the trenches are lined with a dielectric material. A conductive material is disposed in the trenches lining the dielectric material on the sidewalls and the bottom surface. The conductive material on the bottom surface of the trenches is removed so that a first portion of conductive material remains on a first sidewall of each trench, and a second portion of conductive material remains on a second sidewall of each trench. The first and second portions of conductive material are electrically isolated from each other. The space between the first and second portions of the conductive material is filled with a trench filling insulator material and a Schottky contact is formed between the outermost sidewalls of the two trenches.

CLAIM OF PRIORITY

This application is a division of commonly-assigned, co-pendingapplication Ser. No. 13/926,880, (Attorney Docket Number ANO-063/US)filed Jun. 25, 2013, and entitled “MOSFET WITH INTEGRATED SCHOTTKYDIODE”, the entire disclosures of which are incorporated herein byreference.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to commonly-assigned, co-pending applicationSer. No. 13/776,523, (Attorney Docket Number ANO-061/US) filed Feb. 25,2013, and entitled “TERMINATION TRENCH FOR POWER MOSFET APPLICATIONS”,the entire disclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

This invention generally relates to power device structures and a methodfor manufacturing the device thereof. Specifically, the invention isdirected to a method to implement an integrated Schottky diode intosystem that can include both active and passive devices and all thedevices made from the method.

BACKGROUND OF THE INVENTION

Metal-oxide-semiconductor field-effect transistors (MOSFETs) are usedfor amplifying or switching electronic signals. A MOSFET device used forpower switching is sometimes referred to as a power MOSFET. Power MOSFETdevices typically contain multiple individual MOSFET structures arrangedin active cells. The switching frequency of MOSFET devices are limitedby device characteristics, largely capacitances, and in the case ofcertain applications, namely DC-DC converters, the recovery of theparasitic diode inherent in all power MOSFET device structures. In thelatter case, Schottky diodes are commonly connected in parallel to theMOSFET devices to improve the diode recovery portion of the devicesswitching behavior. Additionally, Schottky diodes have an added benefitof a lower forward diode voltage drop, which suppresses power loss inthe non-switching portion of device operation.

However, the use of a Schottky diode in parallel with the MOSFET devicesdoes have some drawbacks. First, Schottky diodes typically have highreverse bias current leakage which adversely affects the performance ofthe device. Additionally, the integration of a Schottky diode into anMOSFET device utilizes valuable space on the die that could otherwise beused for additional active devices. Further, the integration of aSchottky diode may increase the cost of manufacturing the MOSFET devicesbecause additional mask sets may be needed to form the Schottky diode.Therefore, there is a need in the art for a Schottky diode that hasminimal leakage and can be integrated into the device in a spaceconscious manner without needing additional masks.

It is within this context that embodiments of the present inventionarise.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is an overhead view depicting the layout of a device die wherethe Schottky structure is formed in the active area according to anaspect of the present disclosure.

FIGS. 1B-1C are zoomed in views of the Schottky structure shown in FIG.1A according to various aspects of the present disclosure.

FIG. 2A is an overhead view depicting the layout of a device die wherethe Schottky structure is formed in the termination region according toan aspect of the present disclosure.

FIGS. 2B-2C are zoomed in views of the Schottky structure shown in FIG.2A according to various aspects of the present disclosure.

FIGS. 3A-3G are cross-sectional views of the Schottky structureaccording to various aspects of the present disclosure.

FIG. 3H is a top view of the Schottky structure according to one aspectof the present disclosure.

FIG. 3I is a cross-sectional view of FIG. 3H.

FIG. 3J is a top view of the Schottky structure according to one aspectof the present disclosure.

FIG. 3K is a cross-sectional view of FIG. 3J.

FIGS. 4A-4M are cross-sectional views of a Schottky structure duringvarious processing steps according to an aspect of the presentdisclosure.

FIGS. 5A-5B are cross-section views of a Schottky structure duringprocessing according to an additional aspect of the present disclosure.

FIGS. 6A-6B are cross-section views of a Schottky structure duringprocessing according to an additional aspect of the present disclosure.

FIGS. 7A-7B are cross-section views of a Schottky structure duringprocessing according to an additional aspect of the present disclosure.

FIGS. 8A-8B are cross-section views of a Schottky structure duringprocessing according to an additional aspect of the present disclosure.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

Although the following detailed description contains many specificdetails for the purposes of illustration, anyone of ordinary skill inthe art will appreciate that many variations and alterations to thefollowing details are within the scope of the invention. Accordingly,the exemplary embodiments of the invention described below are set forthwithout any loss of generality to, and without imposing limitationsupon, the claimed invention.

In the following Detailed Description, reference is made to theaccompanying drawings, which form a part hereof, and in which is shownby way of illustration specific embodiments in which the invention maybe practiced. In this regard, directional terminology, such as “top,”“bottom,” “front,” “back,” “leading,” “trailing,” “first,” “second,”etc., is used with reference to the orientation of the figure(s) beingdescribed. Because components of embodiments of the present inventioncan be positioned in a number of different orientations, the directionalterminology is used for purposes of illustration and is in no waylimiting. It is to be understood that other embodiments may be utilizedand structural or logical changes may be made without departing from thescope of the present invention. The following detailed description,therefore, is not to be taken in a limiting sense, and the scope of thepresent invention is defined by the appended claims.

Additionally, concentrations, amounts, and other numerical data may bepresented herein in a range format. It is to be understood that suchrange format is used merely for convenience and brevity and should beinterpreted flexibly to include not only the numerical values explicitlyrecited as the limits of the range, but also to include all theindividual numerical values or sub-ranges encompassed within that rangeas if each numerical value and sub-range is explicitly recited. Forexample, a thickness range of about 1 nm to about 200 nm should beinterpreted to include not only the explicitly recited limits of about 1nm and about 200 nm, but also to include individual sizes such as butnot limited to 2 nm, 3 nm, 4 nm, and sub-ranges such as 10 nm to 50 nm,20 nm to 100 nm, etc. that are within the recited limits.

In the following discussion, devices with an N-type epitaxial layer anda P-type top layer are described for purposes of illustration.Substantially similar devices may be fabricated using a similar processbut with opposite conductivity types.

FIG. 1A is an overhead view of a device structure 100 that is formed ona semiconductor substrate 101. The device structure 100 includes anactive area 102 that is formed within the outermost dotted box. Theregion outside of the dotted box may be considered the terminationregion 103. One or more termination trenches may be located in thetermination region. In device structure 100 there is a singletermination trench (not shown) that has two separate conductive portions115A and 115B formed within the trench. One of the conductive portions115A and 115B in the one or more termination trenches may be connectedto a drain contact 108. A conductive portion 115A in a terminationtrench nearest to the active area 102 may be connected to the gatecontact 128. By way of example, and not by way of limitation, thetermination trenches may be substantially similar to terminationtrenches described in related patent application Ser. No. 13/776,523filed Feb. 25, 2013 and entitled “TERMINATION TRENCH FOR POWER MOSFETAPPLICATIONS” by Lee et al, which is incorporated herein in itsentirety.

In the active area 102 the gate electrodes 114 of the active devicestructures are shown. The device trenches in the active area may belined with a dielectric material (not shown) and filled with aconductive material to form gate electrodes 114. The gate electrodes 114may be connected to the gate metal (not shown) with a gate contact 128.The gate electrodes 114 are shown in a striped orientation, butalternative aspects of the present disclosure may also includealternative device layouts, such as, but not limited to a closed cellorientation. The gate contact 128 may be formed with a conductivematerial such as tungsten. Gate contact 128 may extend perpendicular tothe plane of the drawing to make electrical contact with the gate metal(not shown). The gate metal may be initially formed as part of the samemetal layer as the source metal (not shown). The gate metal may beelectrically isolated from the source metal, e.g., by masking, etchingand dielectric fill processes, as are commonly done for this purpose.Additionally, a Schottky structure 180 is formed in the active area 102.In FIG. 1A, only the conductive portions 115A and 115B of the Schottkystructure 180 are shown. A zoomed in overhead view of various Schottkystructures according to various aspects of the present disclosure areshown in FIGS. 1B and 1C.

FIG. 1B depicts two trenches 113 _(A) and 113 _(B) running parallel toeach other. The two trenches may be spaced apart from each other by amesa M. The width of the mesa M may be less than or equal to the widthof a device mesa that separates device trenches from each other. Thewidth of the mesa M may be chosen such that the depletion regions formedalong the sides of the trenches 113 _(A) and 113 _(B) proximate to themesa M merge together to a degree that allows suitable control over ofthe reverse blocking state leakage, but not so constricting as toincrease the diode forward voltage (of the diode) to a considerabledegree, thereby preventing the Schottky diode from functioning as aneffective means to mitigate (power) loss. By way of example, and not byway of limitation, the width of the mesa M may be approximately betweenone-fourth and three-fourths of the width of the mesa between activedevice structures. The sidewalls of each trench may be lined with adielectric material 111. A conductive material 115 may be disposedproximate to each lined trench wall. As such each trench has a first andsecond conductive portion. The two conductive portions 115 in eachtrench are electrically isolated from each other by an insulativematerial 117, such as an oxide. As shown in FIG. 1B the first conductiveportion 115 _(A1) is separated from the second conductive portion 115_(A2) in trench 113 _(A) and the first conductive portion 115 _(B1) isseparated from the second conductive portion 115 _(B2) in trench 113_(B). The conductive portions 115 and the gate electrodes 114 may bemade from the same material, e.g., polysilicon, which may be formed incorresponding trenches in a common step. Between the two trenches theremay be a Schottky contact 182 formed. By way of example, and not by wayof limitation, the Schottky contact 182 may be made of tungsten that isdeposited by CVD.

FIG. 1C depicts an overhead view of a Schottky structure 180′ accordingto an additional aspect of the present disclosure. The structure 180′ issubstantially similar to the Schottky structure 180 except that thelocation of the Schottky contact 182 has been changed. Instead of beingformed in the mesa M, the Schottky contact 182 may be formed between thefirst and second conductive portions 115 _(B1) and 115 _(B2). TheSchottky contact 182 extends through the bottom of the trench 113 _(B)in order to create the contact with the substrate 101 below the trench.While a single Schottky contact 182 is shown in FIG. 1C, aspects of thepresent disclosure also include structures in which there is a Schottkycontact 182 in between the first and second portions 115 in bothtrenches 113 _(A) and 113 _(B). According to yet additional aspects ofthe present disclosure, a Schottky contact 182 may be formed in the mesaM, as shown in FIG. 1B and in between the conductive portions 115 in oneor both trenches 113 _(A) and 113 _(B) Further, while the Schottkystructure 180 is shown as a single strip in FIG. 1A, there may be morethan one strip, or only a portion of a single strip depending on thespecifications of the device 100.

FIG. 2A is an overhead view of an additional aspect of the presentdisclosure, in which the device 200 has a Schottky structure 181 formedin the termination region 103. In FIG. 2A the active device structureswithin the active region 102 may be substantially similar to the activedevice structures described with respect to FIGS. 1A-1C. FIG. 2A depictsonly the conductive portions 115 _(A1), 115 _(A2) of a first trench 113_(A) and conductive portions 115 _(B1) and 115 _(B2) of a second trench113 _(B). Placing the Schottky structure in the termination region 103saves room in the active region 102 for additional active devicestructures. In the example depicted in FIG. 2A, the conductive portions115 _(A2) and 115 _(B1) may be electrically connected to each other byconductive shorts 183 to short the inner conductive portions 115 _(A2)to source potential.

FIG. 2B is a zoomed in look at the termination Schottky structure 181according to an aspect of the present disclosure. Two trenches 113 _(A)and 113 _(B) run parallel to each other. The two trenches may be spacedapart from each other by a mesa M. The width of the mesa M may be lessthan or equal to the width of a device mesa that separates devicetrenches from each other. The width of the mesa M can be chosen suchthat the depletion regions formed along the sides of the trenches 113_(A) and 113 _(B) proximate to the mesa M merge together to a degreethat allows suitable control over of the reverse blocking state leakage,but not so constricting as to increase the diode forward voltage (of thediode) to a considerable degree, thereby preventing the Schottky diodefrom functioning as an effective means to mitigate (power) loss. By wayof example, and not by way of limitation, the width of the mesa M may beapproximately between one-fourth and three-fourths of the width of themesa between active device structures. The sidewalls of each trench maybe lined with a dielectric material 111. A conductive material 115 maybe disposed proximate to each lined trench wall. As such, each trenchhas a first and second conductive portion. The two conductive portions115 in each trench are electrically isolated from each other by aninsulative material 117, such as an oxide. As shown in FIG. 2B the firstconductive portion 115 _(A1) is separated from the second conductiveportion 115 _(A2) in trench 113 _(A) and the first conductive portion115 _(B1) is separated from the second conductive portion 115 _(B2) intrench 113 _(B). The conductive portions 115 and the gate electrodes 114of the active devices may be made from the same material, e.g.,polysilicon, which may be formed in corresponding trenches in a commonstep. Between the two trenches there may be a Schottky contact 182formed. By way of example, and not by way of limitation, the Schottkycontact 182 may be made of tungsten that is deposited by CVD.

FIG. 2C depicts an overhead view of a Schottky structure 181′ accordingto an additional aspect of the present disclosure. The structure 181′ issubstantially similar to the Schottky structure 181 except that thelocation of the Schottky contact 182 is different. Instead of beingformed in the mesa M, the Schottky contact 182 may be formed between thefirst and second conductive portions 115 _(B1) and 115 _(B2). TheSchottky contact 182 extends through the bottom of the trench 113 _(B)in order to create a contact with the substrate 101 below the trench.While a single Schottky contact 182 is shown in FIG. 2C, aspects of thepresent disclosure also include structures in which there is a Schottkycontact 182 in between the first and second portions 115 in bothtrenches 113 _(A) and 113 _(B). According to yet additional aspects ofthe present disclosure, a Schottky contact 182 may be formed in the mesaM, as shown in FIG. 2B and in between the conductive portions 115 in oneor both trenches 113 _(A) and 113 _(B).

FIG. 3A is a cross-sectional view of the Schottky structure 180 alongthe line 3A-3A shown in FIG. 1B. Schottky structure 180 may be formed ona semiconductor substrate 301. Furthermore, a plurality of such Schottkystructures 180 may be formed on the same substrate, as is common insemiconductor manufacturing. The substrate 301 may be suitably doped tobe an N-type or a P-type substrate. By way of example, and not by way oflimitation, the semiconductor substrate 301 may be an N-type siliconsubstrate. The semiconductor substrate may have a heavily doped N⁺ drainregion 305. By way of example, the drain region 305 may have a dopingconcentration of approximately 10¹⁹ cm⁻³ or greater. The drain region305 may be electrically connected to a drain electrode (not shown)formed on a bottom surface of the semiconductor substrate. Above thedrain region 305 may be a lightly doped N⁻ drift region 306. By way ofexample, the drift region 306 may have a doping concentration that isapproximately between about 10¹⁵ cm⁻³ and about 10¹⁷ cm⁻³. Above thedrift region 306, except for in the mesa portion M, a suitably dopedbody layer 319 of a second conductivity type that is opposite to thefirst conductivity type of the semiconductor substrate may be formed. Asource region 320 of the first conductivity type may be formed in a topportion of the body layer 319. By way of example, and as used throughoutthe remainder of the disclosure, the semiconductor substrate 301 may bean N-type semiconductor, the body region 319 may be a P-type, and thesource region 320 may be N-type.

Two trenches 313 _(A) and 313 _(B) are formed into the substrate 301.The depth of the trenches 313 _(A) and 313 _(B) may be substantiallysimilar to the depth of device trenches formed in the active area 102.The width of trenches 313 _(A) and 313 _(B) is wider than the width ofthe active device structures. The width of the trenches 313 in theSchottky structure 180 may be chosen such that when the device trenchesare filled with a trench filling material to form the gate electrodes114, the trench filling material will only line the sidewalls and bottomof the trenches 313 _(A) and 313 _(B). By way of example, and not by wayof limitation, trenches 313 _(A) and 313 _(B) may be at least twice aswide as the device trenches, e.g., if the device trenches areapproximately 0.5 microns wide, then the trenches 313 _(A) and 313 _(B)may be approximately 1.0 microns wide or greater. Each trench 313 _(A)and 313 _(B) may have an upper portion 373 and a bottom portion 374. Adielectric material 311 may line the walls of the trench. The dielectricmaterial 311 may have a thickness T₂ in the bottom portion of the trench374 and the dielectric material 311 may have a thickness T₁ in the upperportion of the trench 373. According to aspects of the presentdisclosure, the thickness T₁ is smaller than the thickness T₂.

The trench filling material that lines the side wall of the trench 313_(A) furthest from the mesa M may be referred to as the first portion ofthe conductive material 315 _(A1) and the trench filling material thatlines the wall of the trench 315 _(A) proximate to the mesa M may bereferred to as the second portion of the conductive material 315 _(A2).The trench filling material that lines the side wall of the trench 313_(B) closest from the mesa M may be referred to as the first portion ofthe conductive material 315 _(B1) and the trench filling material thatlines the wall of the trench 315 _(B) furthest from the mesa M may bereferred to as the second portion of the conductive material 315 _(B2).

In each trench the first and second portions of the conductive materialare electrically isolated from each other by an insulative material 317.By way of example, the insulative material 317 may be an oxide.Electrically insulating the first and second portions of conductivematerial from each other allows for each portion to be maintained at anindependent voltage.

When the Schottky structure 180 is integrated into the active area ofthe device 100 it is desirable that the outermost conductive portions(i.e., the first conductive portion 315 _(A1) in trench 313 _(A), andthe second conductive portion 315 _(B2) in trench 313 _(B)) aremaintained at gate potential. This allows for an active transistordevice to be formed between the Schottky structure 180 and the devicetrenches formed adjacent to the Schottky structure 180. The interiorconductive portions (i.e., the second conductive portion 315 _(A2) intrench 313 _(A) and the first conductive portion 315 _(B1) in trench 313_(B)) may be maintained at the source potential. Since the interiorconductive portions 315 _(A2), 315 _(B1) extend the complete length ofthe trench, shielding for the Schottky contact may be maximized.

According to additional aspects of the present disclosure, an electricalfield line tuning region 316 may be optionally formed beneath thetrenches. The electrical field line tuning region 316 may be formed bydoping the semiconductor substrate 301 below the trenches 313 with aP-type dopant, such as boron. The implantation dose may be adjusted tofurther control the distribution of the electrical field lines presentin the Schottky structure 180. For example, boron can be implanted witha dose in a range of 2e¹¹ to 5e¹² atoms/cm² at an energy of about 30 to80 KeV.

A first insulative spacer 321 may be disposed along each vertical edgeof the insulative material 317 above the insulative layer 322. By way ofexample, and not by way of limitation, the first insulative spacer 321may be the same material as the insulative material 317. Additionally, asecond insulative layer 323 may be formed above the insulative material317 and along the exposed sidewalls of the first insulative spacer 321.By way of example, and not by way of limitation, the first insulativespacer 321 may be made of a material that will resist an etchant thatselectively removes the material that the second insulative layer 323 ismade from. By way of example, the first insulative spacer 321 may be anoxide, and the second insulative layer 323 may be a nitride. The oxideis resistant to a hot phosphoric acid, while the nitride would beselectively etched away by the hot phosphoric acid. Additionally, thefirst insulative spacer 321 and the second insulative layer 323 may bemade from the same insulative material, such as a nitride.

The combination of the first insulative spacers 321 and the secondinsulative layer 323 that are formed along the exposed sidewall of thefirst insulative spacer 321 above the outermost conductive portions 315_(A1), 315 _(B2) allow for vertical connections 329 to be self-alignedbetween the Schottky structure 180 and the device trenches formedadjacent to the Schottky structure 180. An outer insulator 324 may beformed above the second insulative layer 323. By way of example, and notby way of limitation, the outer insulator 324 may be BPSG.

Between the trenches 313 _(A), 313 _(B) a Schottky contact 382 may beformed. The Schottky contact 382 connects the source metal layer 331 tothe substrate 301. By way of example, and not by way of limitation, theSchottky contact 382 may be made from a conductive material such astungsten. According to some aspects of the present disclosure, theSchottky contact 382 may be lined with a barrier metal 383 such astitanium, or a titanium nitride. By placing the Schottky contact 382between the two trenches, the leakage of the Schottky diode may bereduced by the coupling between the trenches 313 _(A) and 313 _(B). Inorder to improve the performance of the Schottky contact, dopants may beimplanted into the substrate 301 near the Schottky contact to form aSchottky tuning region 384. Both N and P type dopants may be used toadjust the characteristics of the Schottky diode.

FIG. 3B is a cross-sectional view of the Schottky structure 180′ alongthe line 3B-3B shown in FIG. 1C. The Schottky structure 180′ issubstantially similar to that of Schottky structure 180 shown in FIG.3A, except for the location of the Schottky contact 382. The Schottkycontact 382 is formed through the bottom of trench 313 _(B). In additionto the first and second portions of conductive material 315 _(B1), 315_(B2) formed in trench 315 _(B), a vertical connection may be madethrough the insulative material 317 to form the Schottky contact 382.The Schottky contact may be electrically connected to the source metal331 and extend through the outer insulator 324, the second insulativelayer 323, the trench insulator 317, and the dielectric material 311,thereby connecting the source metal 331 to the drift region 306 and/orthe field tuning region 316 below the trench structure. Additionally,dopants may be inserted at the bottom of the trench to create a Schottkytuning region 384 in order to improve the performance of the Schottkydiode.

FIG. 3C is a cross-sectional view of a Schottky structure 181 along theline 3C-3C shown in FIG. 2B. The Schottky structure 181 is substantiallysimilar to that of the Schottky structure 180 shown in FIG. 3A, with theexception of the potentials that the conductive portions 315 aremaintained. Since Schottky structure 181 is formed in the terminationregion, the outermost conductive portion 315 _(B2) furthest from theactive area 102 is maintained at the drain potential. The conductiveportion 315 _(A1) nearest to the active area 102 may be maintained atgate potential. The two conductive portions 315 _(A2), 315 _(B1)proximate to the mesa M may be maintained at source potential. This maybe accomplished using conductive shorting structures, e.g., as depictedin FIG. 2A. Additionally, since the Schottky structure 181 is in thetermination region 103, the source 320 and body layers 319 formedoutside of the Schottky structure may be omitted. However, in order toallow the active device closest to the termination structure to be afunctioning device, the source 319 and body layers 320 may be formedadjacent to the trench 315 _(A).

FIG. 3D is a cross-sectional view of the Schottky structure 181′ alongthe line 3D-3D shown in FIG. 2C. The Schottky structure 181′ issubstantially similar to that of Schottky structure 181 shown in FIG.3C, except for the location of the Schottky contact 382. The Schottkycontact 382 is formed through the bottom of trench 313 _(B). In additionto the first and second portions of conductive material 315 _(B1), 315_(B2) formed in trench 315 _(B), a vertical connection may be madethrough the insulative material 317 to form the Schottky contact 382.The Schottky contact 382 may be electrically connected to the sourcemetal 331 and extend through the outer insulator 324, the secondinsulative layer 323, the trench insulator 317, and the dielectricmaterial 311, thereby connecting the source metal 331 to the driftregion 306 and/or the field tuning region 316 below the trench structure313 _(B). Additionally, dopants may be inserted at the bottom of thetrench to create a Schottky tuning region 384 in order to improve theperformance of the Schottky diode.

FIG. 3E is a cross-sectional view of a Schottky structure 180″ accordingto an additional aspect of the present disclosure. Schottky structure180″ is substantially similar to Schottky structure 180′ shown in FIG.3B with an additional Schottky contact 182 formed in trench 313 _(A).The additional Schottky contact 382 may include a Schottky tuning region384. Alternatively, one or both of the Schottky tuning regions 384 maybe replaced with dopants that would disable the Schottky diode. As such,the same mask sets may be used to fabricate a device with one, two, orzero Schottky diodes. In one example, P-type dopants would be used todisable the Schottky contact. Specially, a p-type dose (e.g. Boron)sufficient to bring the surface concentration to greater than about1e18/cm³ would be sufficient to disable the Schottky contact.

FIG. 3F is a cross-sectional view of a Schottky structure 180′″according to another additional aspect of the present disclosure.Schottky structure 180′″ is substantially similar to Schottky structure180 with an additional Schottky contact 382 incorporated. The secondSchottky contact 382 is substantially similar to the Schottky contact382 utilized in Schottky structure 180′. As such, a Schottky structure180′″ may utilize Schottky contacts located at the mesa M and thesubstrate 301 below one or both trenches 313 _(A) and/or 313 _(B).

In FIGS. 3A-3F the interior conductive portions (e.g., 315 _(A2) and 315_(B1)) are maintained at source potential by a connection in a thirddimension that is not shown in the cross-sectional views. In accordancewith additional aspects of the present disclosure, the connection to thesource metal may be made in the cross-sectional view shown in thefigures. Schottky structure 185 shown in FIG. 3G is such a device.Instead of making a connection in the third dimension, the Schottkycontact 182 may be widened in order to partially etch through a portionof the insulative material 317 in the trenches 313 _(A), 313 _(B). Assuch, the source metal 331 is also connected to the second conductiveportion 315 _(A2) of trench 313 _(A) and to the first conductive portion315 _(B1) of trench 313 _(B). The outer insulative lining 311 along thesidewalls of the trenches remains in place.

FIGS. 3H-3K shows examples of closed cell Schottky structures accordingto aspects of the present disclosure. FIG. 3H is a top view of a firstclosed cell Schottky structure and FIG. 3I is a cross-sectional view ofthe structure shown in FIG. 3H along the line 3H-3H. The structure shownin FIGS. 3H-3I is similar to that depicted in cross-section in FIG. 3A,FIG. 3C and FIG. 3F. However, unlike the structure shown in FIG. 1B andFIG. 2B, the Schottky contact 382′ between the trenches 315 _(A),315_(B) is not a continuous stripe. Instead, as may be seen in FIG. 3H, theSchottky contact 382′ between trenches 315 _(A), 315 _(B) is a shortclosed cell vertical contact and the trenches and separate conductiveportions 315 _(A2), 315 _(B1) are configured to detour around theshortened Schottky contact 382′.

FIG. 3J is a top view of an alternative closed cell Schottky structureand FIG. 3K is a corresponding cross-sectional view of the structure ofFIG. 3J taken along the line 3J-3J. The structure shown in FIGS. 3J-3Kis similar to that depicted in cross-section in FIG. 3G. In particular,the closed cell Schottky structure of FIG. 3J includes a Schottkycontact 382′ between the trenches 315 _(A), 315 _(B). The Schottkycontact 382′ overlaps the conductive portions 315 _(AB). However, theSchottky contact 382′ between the trenches 315 _(A),315 _(B) is not acontinuous stripe. Furthermore, the Schottky contact 382′ is surroundedby a conductive portion 315 _(AB) that is electrically connected tosource potential forming a closed-cell Schottky contact.

FIGS. 4A-4M depict a method for forming a device 100 according to anaspect of the present disclosure where the Schottky structure is formedin the active area 102.

FIG. 4A depicts a semiconductor device structure 100. The devicestructure may be formed on a substrate 301 that may be suitably doped tobe an N-type or a P-type substrate. By way of example, and not by way oflimitation, the semiconductor substrate 301 may be an N-type siliconsubstrate. As used herein, the substrate of device structure 100 will bedescribed as an N-type silicon substrate. The semiconductor substrate301 may comprise a lightly doped drift region 306 formed in an upperportion of the substrate and a heavily doped drain contact region 305formed on a bottom portion of the semiconductor substrate. Anoxide-nitride-oxide (ONO) hard mask layer may be formed on a top of thelightly doped drift region 306. By way of example and not by way oflimitation, the bottom oxide layer 307 may be approximately 200 Å, thenitride layer 308 may be approximately 3500 Å, and the top upper oxidelayer 309 may be approximately 1400 Å.

FIG. 4B depicts the device structure 100 after several initialprocessing steps. First, a trench mask and etching process may be usedto form an upper portion of the trenches 313 _(A) and 313 _(B). A trenchetching process may comprise an etchant to remove the ONO hard masklayer 307, 308, 309, in order to expose the top surface of the substrateand a second etching process to form the upper portion of trenches 313_(A) and 313 _(B). By way of example, and not by way of limitation, theupper portion of trenches 313 _(A) and 313 _(B) may be approximately 0.5μm deep. Trenches 313 _(A) and 313 _(B) may be wider than the trenchesused in the active device structures in the active area 102. The widthof the trenches 313 _(A) and 313 _(B) may be chosen such that the devicetrenches in the active area will completely fill with a conductivematerial during a subsequent trench filling process, whereas the sametrench filling process will only cause trenches 313 _(A) and 313 _(B) tobe lined with the conductive material. By way of example, and not by wayof limitation, the trenches 313 _(A) and 313 _(B) may be twice as largeas the device trenches. Once the trenches have been formed, a pad oxide311 _(a) may be thermally grown in each trench 313 that is approximately100 Å thick. After the pad oxide 311 _(a) has been grown, a nitridelayer 312 may be deposited over the pad oxide 311 _(a). By way ofexample, and not by way of limitation, the nitride layer 312 may beapproximately 500 Å thick.

FIG. 4C depicts the formation of the bottom portion of the trenches.First, the nitride layer 312 and the oxide layer 311 _(a) on the bottomsurface of the trench may be removed with one or more etching processes.Thereafter, the drift region 306 below the upper portion of the trenchesmay be etched to increase the depth of the trenches 313 _(A) and 313_(B). By way of example, and not by way of limitation, the combineddepth of the upper and bottom portions of the trenches may beapproximately 1.0 μm. Further by way of example, and not by way oflimitation, the aspect ratio of the trenches 313 (i.e., the depth of thetrench divided by the width of the trench) may be between 1 and 100.Thereafter, a liner oxide 311 _(b) is thermally grown in the exposedsilicon at the bottom portion of the trenches. By way of example, theliner oxide 311 _(b) in the bottom portion of the trenches 313 may begrown to a thickness T₂ that is approximately 600 Å. The nitride layer312 along the walls of the upper portion of the trench functions as amask, and reduces the width of the bottom portion of the trench.

In FIG. 4D the nitride 312 and the pad oxide 311 _(a) at the side wallof the upper portion of the trench are then removed by a wet dip. Then agate oxide 311 _(c) is grown on the exposed silicon at the side wall ofthe upper portion of the trenches 313 to a desired thickness T₁. By wayof example, and not by way of limitation, the thicknesses T₁ of theoxide 311 _(c) may be approximately 265 Å for a 12V device. Therefore,the oxides 311 may have a thickness T₂ in the bottom portion of thetrench that is larger than the thickness T₁ of the upper portion of thetrench. While the above description describes a thickness of the oxide311 as being variable with respect to depth in the trench, it is withinthe scope of the present disclosure to have a uniform gate oxidethickness 311.

Next, in FIG. 4D the trenches 313 are partially filled with a conductivematerial 315. By way of example, and not by way of limitation,conductive material may be an N⁺-doped polysilicon, and the polysiliconmay be deposited through chemical vapor deposition (CVD). Thisdeposition of the conductive material 315 into the trenches may be doneat the same time the gate electrodes 114 are formed in the active area102. Since the trenches 313 are wider than the trenches for the gateelectrodes 114, the conductive material 315 in the trenches 313 willonly line the bottom portion and the side walls. It is noted that forthe sake of clarity, cross-sectional details of the trench and gateelectrode 114 for an device have been omitted. Detailed examples ofconfiguration and fabrication of active devices are described and shownin detail in commonly assigned, co-pending U.S. patent application Ser.No. 13/776,523, (attorney docket no. ANO-061/US) filed Feb. 25, 2013 andfully incorporated herein by reference.

In FIG. 4E the conductive material 315 may be planarized with thesurface of the hard mask using chemical mechanical polishing (CMP).Next, as shown in FIG. 4E, the conductive material 315 may be etchedback to the surface of the semiconductor substrate. By way of exampleand not by way of limitation, the etching may be performed with a dryetching process. During this process, the conductive material 315 liningthe bottom portion of the trenches 313 may be removed, thereby formingtwo separate portions of conductive material in each trench. As usedherein, in the first trench 313 _(A) the first conductive portion islabeled 315 _(A1) and the second conductive portion is labeled 315_(A2). As used herein, in the second trench 313 _(B) the firstconductive portion is labeled 315 _(B1) and the second conductiveportion is labeled 315 _(B2). Electrically insulating the first andsecond portions of conductive material from each other allows for eachportion to be maintained at an independent voltage. When the Schottkystructure 180 is integrated into the active area of the device 100 it isdesirable that the outermost conductive portions (i.e., the firstconductive portion 315 _(A1) in trench 313 _(A), and the secondconductive portion 315 _(B2) in trench 313 _(B)) are maintained at gatepotential. This allows for an active transistor device, e.g., a MOSFETdevice, bipolar transistor, insulated gate bipolar transistor, junctionfield effect transistor, or diode or, an inactive device, such as aresistor or capacitor, to be formed between the Schottky structure 180and the device trenches formed adjacent to the Schottky structure 180.The interior conductive portions (i.e., the second conductive portion315 _(A2) in trench 313 _(A) and the first conductive portion 315 _(B1)in trench 313 _(B)) may be maintained at the source potential. Since theinterior conductive portions 315 _(A2), 315 _(B1) extend the completelength of the trench, shielding for the Schottky contact may bemaximized.

According to an additional aspect of the present disclosure, in which adevice 200 includes a Schottky structure 181 that is located in thetermination region 103 (as shown in FIG. 3C), the potentials of theconductive portions may be varied. Since Schottky structure 181 isformed in the termination region, the outermost conductive portion 315_(B2) furthest from the active area 102 is maintained at the drainpotential. The conductive portion 315 _(A1) nearest to the active area102 may be maintained at gate potential. The two conductive portions 315_(A2), 315 _(B1) proximate to the mesa M may be maintained at sourcepotential.

Additionally, a field line tuning region 316 may be formed below thetrenches 313 _(A), 313 _(B) after the conductive material 315 at thebottom of the trenches 313 has been removed. The field line tuningregion 316 may be formed by implanting dopants of the conductivity typeopposite that of the drift region 306. By way of example, and not by wayof limitation, boron can be implanted with a dose in a range of 2e¹¹ to5e¹² atoms/cm² at an energy of about 30 to 80 KeV.

In FIG. 4F the trenches 313 _(A), 313 _(B) are filled with theinsulative material 317. By way of example, and not by way oflimitation, the insulative material 317 may be an oxide. The insulativematerial 317 electrically separates the first and second portions of theconductive trench material 315 _(A1) and 315 _(A2) in trench 313 _(A),and the first and second portions of the conductive trench material 315_(B1) and 315 _(B2). Once the insulative material 317 has been formed,the top oxide layer 309 of the ONO hardmask may be removed by CMP. Theinsulative material 317 may also be planarized with the nitride layer308 with CMP.

In FIG. 4G the nitride layer 308 of the ONO hardmask may be removed. Byway of example, the hardmask may be selectively removed with ahot-phosphoric acid wet dip. Thereafter, the body region 319 may beformed. By way of example, and not by way of limitation, the body region319 may be formed with a body mask and a blanket implantation, orthrough selectively implanting ions with an ion implantation system.FIG. 4G also shows the formation of the source region 320. By way ofexample, and not by way of limitation, the source region 320 may beformed with a source mask and a blanket source implantation, or throughselectively implanting ions with an ion implantation system. The mesa Mbetween the trenches 313 may be blocked from receiving the body implantand the source implant.

FIG. 4G′ depicts the formation of the source and body regions accordingto an additional aspect of the present disclosure, in which a device 200includes a Schottky structure 181 that is located in the terminationregion 103 (as shown in FIG. 3C). The body and source masks may alsoprevent the dopants from being implanted proximate to the outermostconductive portion 315 _(B2). The subsequent processing of Schottkystructure 181 is substantially similar to that of Schottky structure 180after the source and body implants.

FIG. 4H depicts the deposition of a thick sacrificial insulation layer321′. By way of example, the sacrificial insulation layer may beapproximately 1,100 Å thick. Further by way of example, the insulationlayer 321′ may be an oxide deposited by CVD with a source gas such asTEOS. Alternatively, the insulation layer 321′ may be a nitride materialthat is deposited with a CVD process using a SiH₄ and NH₃ gas mixture.Next, in FIG. 4I the thick insulation layer 321′ may be etched using ananisotropic etch, such as a dry etching process, in order to form thefirst insulating spacers 321 along the sides of the exposed insulativematerial 317.

By way of example, the insulation spacers 321 may be approximately 1000Å thick. When the insulation layer 321′ is an oxide, the etching processmay stop on the silicon substrate's surface, thus removing portions ofthe bottom oxide layer 307 from the ONO hardmask that are not locatedbelow the first insulating spacers 321. A pad oxide 322 may then begrown over the surface of the substrate. By way of example, and not byway of limitation, the pad oxide 322 may be approximately 100 Å thick.

Alternatively, a similar process may be used for forming the firstinsulating spacers 321 in a device that utilizes a sacrificialinsulation layer 321′ that is a nitride material. In this situation theanisotropic etching process may selectively etch away the nitridematerial and leave the bottom oxide layer 307 of the ONO hardmask inplace. As such, there is no need to grow the pad oxide 322. Once thefirst insulating spacers 321 have been formed, the processing of adevice that has first insulating spacers that are made from a nitridematerial would then continue in substantially the same manner as thatdescribed for a process where the first insulating spacers 321 are madefrom an oxide.

After the first insulating spacers 321 have been formed, a sacrificialnitride layer 323 may be deposited over the surface as shown in FIG. 4J.By way of example, the nitride layer 323 may be approximately 300 Åthick. The nitride layer 323 may be deposited with a CVD process using aSiH₄ and NH₃ gas mixture. As shown in FIG. 4K, a thick layer ofborophosphosilicate glass (BPSG) 324 may then be deposited over thenitride layer 323 with a CVD process.

A contact mask may be used in FIG. 4L to form a Schottky trench 325 thatprovides access for conductive vertical connections to reach the mesa Min order to form a Schottky contact 382. The etching process may utilizethree separate etching steps. First, an etchant may be used that willremove the BPSG layer 324 and will not remove the nitride layer 323below the BPSG. This allows for a fast etch, since there is no chance ofover etching due to the nitride stop layer 323. A second etchant maythen be used to selectively etch through the nitride layer 323.Thereafter, a third etchant may be used that has a high selectivity foroxide in order to break through the pad oxide layer 322. Additionally, aSchottky tuning region 384 may be formed at the top surface of the mesaM. By way of example, and not by way of limitation, the Schottky tuningregion 384 may be formed by implanting dopants into the top surface ofthe Mesa. The implant used to tune the Schottky performance, sometimesreferred to as a Shannon implant, may be designed to adjust the barrierheight of the Schottky interface. This is usually done by lowering, butnot inverting, the local dopant concentration at the metal-siliconinterface. In such a case, the implant species is that opposite to thatof the lightly doped drift region. For the case of an n-type driftlayer, the implant would be boron or BF₂ with a dose in the range ofabout 1e11 to about 1e12 at energy of about 30 KeV. This is an exampleonly, and other combinations of the implant parameters, which wouldachieve the same goal, are certainly possible.

In FIG. 4M a barrier metal 383 may be deposited over the surface of theSchottky trench 325. By way of example, and not by way of limitation,the barrier metal may be titanium that is deposited through physicalvapor deposition (PVD), or it may be an alloy such as TiN which may bedeposited by CVD or PVD. After the barrier metal has been deposited, aconductive material may be deposited in order to form the Schottkycontact 382. By way of example, and not by way of limitation, theSchottky contact 382 may be made of tungsten that is deposited by CVD.Once the layer of tungsten has been deposited, it may be etched back inorder to leave the tungsten primarily in the vertical contact holes.Metal may then be deposited over the entire surface to provideappropriate contacts to source and the gate. Finally, a metal mask maybe used to etch away portions of the deposited metal in order toelectrically isolate the contact areas into a source metal 331, and agate metal (not shown).

FIGS. 5A-5B depict additional steps that may be utilized in order toform a device 100 with a Schottky structure 180′ that is shown in FIG.3B. Device 100′ follows the same processing flow described in FIGS.4A-4K. However, instead of forming the Schottky trench 325 above themesa M, the Schottky trench is formed through the center of each trench313 _(B) as shown in FIG. 5A. A Schottky tuning region 384 may beimplanted at the bottom of the Schottky trench 325. A properly dopedSchottky tuning region will allow the Schottky contact to functionproperly. However, if the doping concentration is altered in theSchottky tuning region, then the Schottky contact may be optionallydeactivated. This is beneficial because it allows for a device with orwithout a Schottky contact to be formed with a single mask set.

After the Schottky trench 325 has been formed and the desired dopantshave been implanted into the Schottky tuning region, the Schottkycontacts may be formed. In FIG. 5B a barrier metal 383 may be disposedon the sidewalls and bottom surface of the trench 325. By way ofexample, and not by way of limitation, the barrier metal may be titaniumthat is deposited through physical vapor deposition (PVD), or it may bean alloy such as TiN which may be deposited by CVD or PVD. After thebarrier metal has been deposited, a conductive material may be depositedin order to form the Schottky contact 382. By way of example, and not byway of limitation, the Schottky contact 382 may be made of tungsten thatis deposited by CVD. Once the layer of tungsten has been deposited, itmay be etched back in order to leave the tungsten primarily in thevertical contact holes. Metal may then be deposited over the entiresurface to provide appropriate contacts to source and the gate. Finally,a metal mask may be used to etch away portions of the deposited metal inorder to electrically isolate the contact areas into a source metal 331,and a gate metal (not shown).

FIGS. 6A-6B depict additional steps that may be utilized in order toform a device 100 with a Schottky structure 180″ that is shown in FIG.3E. Schottky structure 180″ follows the same processing flow describedin FIGS. 4A-4K. However, instead of forming the Schottky trench 325above the mesa M, two Schottky trenches are formed through the center ofeach trench 313 _(A) and 313 _(B) as shown in FIG. 6A. A Schottky tuningregion 384 may be implanted at the bottom one or both of each Schottkytrenches 325. The control of the doping at the bottom of the trenchallows for there to be one, two, or zero Schottky contacts in thedevice. A properly doped Schottky tuning region will allow the Schottkycontact to function properly. However, if the doping concentration isaltered in the Schottky tuning region, then the Schottky contact may beoptionally deactivated. This is beneficial because it allows fordifferent numbers of Schottky contacts to be formed with a single maskset.

After the Schottky trenches 325 have been formed and the desired dopantshave been implanted into the Schottky tuning region, the Schottkycontacts may be formed. In FIG. 6B a barrier metal 383 may be disposedon the sidewalls and bottom surface of the trenches 325. By way ofexample, and not by way of limitation, the barrier metal may be titaniumthat is deposited through physical vapor deposition (PVD), or it may bean alloy such as TiN which may be deposited by CVD or PVD. After thebarrier metal has been deposited, a conductive material may be depositedin order to form the Schottky contact 382. By way of example, and not byway of limitation, the Schottky contact 382 may be made of tungsten thatis deposited by CVD. Once the layer of tungsten has been deposited, itmay be etched back in order to leave the tungsten primarily in thevertical contact holes. Metal may then be deposited over the entiresurface to provide appropriate contacts to source and the gate. Finally,a metal mask may be used to etch away portions of the deposited metal inorder to electrically isolate the contact areas into a source metal 331,and a gate metal (not shown).

FIGS. 7A-7B depict additional steps that may be utilized in order toform a device 100 with a Schottky structure 180′″ that is shown in FIG.3F. Schottky structure 180′″ follows the same processing flow describedin FIGS. 4A-4K. However, instead of forming the Schottky trench 325 onlyabove the mesa M, an additional Schottky trench may be formed throughthe center of one or both trenches 313 _(A) and 313 _(B) as shown inFIG. 7A. Once the trenches 325 have been formed the processing continuesin substantially the same manner described above with respect to formingthe Schottky contacts 382. FIG. 7B depicts the finished Schottkystructure 180′″ with a Schottky contact 382 contacting the mesa M andcontacting the substrate 301 below the trench 313 _(B). Similar to theSchottky contacts described in alternative aspects of the presentdisclosure, the Schottky trenches 325 may be lined with a barrier metal383, and a Schottky tuning region 384 may be formed below the Schottkycontacts.

FIGS. 8A-8B depict additional steps that may be utilized in order toform a device 100 with a Schottky structure 185 that is shown in FIG.3G. Schottky structure 185 follows the same processing flow described inFIGS. 4A-4K. However, instead of forming the Schottky trench 325 onlyabove the mesa M, the Schottky trench 325 is made wider in order to makeelectrical contact with the second portion of conductive material 315_(A2) in trench 313 _(A), and with the first portion of conductivematerial 315 _(B1) in trench 313 _(B), as shown in FIG. 8A. FIG. 8Bdepicts the finished Schottky structure 185 with a Schottky contact 382contacting the mesa M and contacting the conductive portions 315 _(A2)and 315 _(B1). Similar to the Schottky contacts described in alternativeaspects of the present disclosure, the Schottky trench 325 may be linedwith a barrier metal 383, and a Schottky tuning region 384 may be formedbelow the Schottky contact in the mesa M.

The present disclosure describes a device structure and method toimplement an integrated Schottky diode into system that can include bothactive and passive devices. By way of example, but not limitation, apower MOSFET has been selected to by the primary active device for thisdisclosure, due to its ubiquity in the industry and importance in powerelectronics. Any device structure constructed from the method describedin this disclosure would be a candidate for integration with a Schottkydiode as described herein. Such devices include, but are not limited to,active devices such as bipolar transistors, insulated gate bipolartransistors (IGBTs), junction field effect transistors (JFETs) anddiodes and passive devices such as resistors and capacitors. While theabove is a complete description of the preferred embodiment of thepresent invention, it is possible to use various alternatives,modifications and equivalents. Therefore, the scope of the presentinvention should be determined not with reference to the abovedescription but should, instead, be determined with reference to theappended claims, along with their full scope of equivalents. Anyfeature, whether preferred or not, may be combined with any otherfeature, whether preferred or not. In the claims that follow, theindefinite article “A”, or “An” refers to a quantity of one or more ofthe item following the article, except where expressly stated otherwise.The appended claims are not to be interpreted as includingmeans-plus-function limitations, unless such a limitation is explicitlyrecited in a given claim using the phrase “means for.”

What is claimed is:
 1. A method for forming Schottky structurecomprising: a) forming two trenches in a semiconductor materialseparated by a mesa; b) lining sidewalls and a bottom surface of thetrenches with a dielectric material; c) disposing a conductive materialin the trenches, wherein the disposed conductive material lines thedielectric material on the sidewalls and the bottom surface; d) removingthe conductive material on the bottom surface of the trenches, wherein afirst portion of conductive material remains on a first sidewall of eachtrench, and wherein a second portion of conductive material remains on asecond sidewall of each trench, and wherein the first and secondportions of conductive material are electrically isolated from eachother; e) filling the space between the first and second portions of theconductive material with a trench filling insulator material; and f)forming a Schottky contact between the outermost sidewalls of the twotrenches.
 2. The method of claim 1, wherein the two trenches are formedin an active region of a MOSFET device.
 3. The method of claim 2,wherein the first portion of conductive material in the first trench ismaintained at a gate potential, the second portion of conductivematerial in the first trench is maintained at a source potential, thefirst portion of conductive material in the second trench is maintainedat the source potential, and the second portion of conductive materialin the second trench is maintained at the gate potential.
 4. The methodof claim 1, wherein the two trenches are formed in a termination regionof a MOSFET device.
 5. The method of claim 4, wherein the first portionof conductive material in the first trench is maintained at a gatepotential, the second portion of conductive material in the first trenchis maintained at a source potential, the first portion of conductivematerial in the second trench is maintained at the source potential, andthe second portion of conductive material in the second trench ismaintained at drain potential.
 6. The method of claim 1, wherein a widthof the mesa between the two trenches is equal to a width of a mesabetween device trenches formed in the semiconductor material.
 7. Themethod of claim 1, wherein a width of the mesa between the two trenchesis smaller than an active device mesa separating device trenches.
 8. Themethod of claim 7, wherein the width of the mesa between the twotrenches is between one fourth and three fourths of the width of theactive device mesa.
 9. The method of claim 1, wherein the Schottkycontact is formed in the mesa between the two trenches.
 10. The methodof claim 9, wherein the Schottky contact further contacts the conductiveportions in each trench proximate to the mesa.
 11. The method of claim1, wherein the Schottky contact is formed in one of the trenches betweenthe first conductive portion and the second conductive portion.
 12. Themethod of claim 1, wherein Schottky contacts are formed in both trenchesbetween the first conductive portions and the second conductiveportions.
 13. The method of claim 12, wherein at least one of theSchottky contacts is deactivated by selectively doping the semiconductormaterial below one of the trenches with dopants configured to prevent aSchottky diode from forming.
 14. The method of claim 1, wherein a firstSchottky contact is formed in the mesa between the two trenches and asecond Schottky contact is formed in at least one of the trenchesbetween the first conductive portion and the second conductive portion.15. The method of claim 1, wherein the Schottky structure is integratedinto a bipolar transistor, insulated gate bipolar transistor (IGBT),junction field effect transistor (JFET), a diode, a resistor or acapacitor.